Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Determination of position location may be important for many different types of equipments, particularly for user equipment in a cellular radio system. In a typical cellular radio system, the user equipment communicates via a radio access network (RAN) to one or more core networks. The radio access network covers a geographical area which is divided into cell area, with each cell area being served by a base station, e.g., a radio base station (RBS). Each cell may be further divided into sectors. In some networks a base station may also be called as a “NodeB” (UMTS) or “eNodeB” (LTE). A cell is a geographical area where radio coverage is provided by the RBS. Each cell is identified by an identity within the local radio area, the identity being broadcast in the cell. The base station communicates over the air interface with the UE within range of the base station. In some radio access networks, several base stations are typically connected to a controller node (such as a radio network controller (RNC)) which supervises and coordinates various activities of the plurality of base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
There have already proposed several algorithms for user equipment positioning in a cellular radio system including, among others, Cell Identity (cell ID), round trip time (RTT) positioning, and UE based assisted GPS (A-GPS). The cell ID method simply determines which cell the user equipment is located by identifying the cell to which a received cell ID is associated. Accordingly, the accuracy of the cell ID method is limited by the size of the cell, something that prevents it from being used in more sophisticated applications. RTT positioning method operates by measuring the distance between the antenna of a cell and the UE. This distance restricts the UE location to a circular strip around the base station's antenna. A Polygon To Ellipse Transformation Algorithm can be used together with the cell polygon of the cell to calculate the position of the UE.
The A-GPS positioning method is the most accurate method of the three methods mentioned herein. The A-GPS positioning method needs the UE to be located be equipped with a GPS receiver. As compared to a common GPS positioning method, the A-GPS positioning method makes use of assistance data that allows the UE to improve its performance. The assistance data is composed of GPS time, Ephemeris, Ionospheric corrections, a list over bad satellites, GPS time (accurate to +/−2 seconds) and a UE reference position that is determined with the cell ID positioning method.
The following table shows the normal response time and accuracy for the three methods.
TABLE 1response time and accuracy of three methodsFor Cell-ID method, RNC can get a response within 1.5 s, butthe accuracy is poor and depends on the coverage size of cell.The accuracy is in a range of about 500 meters or more.In some cases, such accuracy is useless.Typical Response TimeMethod(RNC centric)AccuracyCell Id<1.5 spoor, depending on the sizeMeasurement Time: 1 sof the cell(if more than 1 radio links,get Best Cell)RTT<3 smore accurate than CELL IDMeasurement Time:70-100 meters (67%)RNC->UE: 1 s (Best cell)150-200 meters (97%)RNC->UE: 1 s (RxTx)RNC->RBS: 1.5 s (RTT)A-GPS<24 smost accurateMeasurement Time: 20 s50 meters (67%)150 meters (97%)
For RTT positioning method, RNC can get a response within 3 s, and the accuracy is much better than Cell-ID method. However, the accuracy is not good enough to be used in some more sophisticated cases.
For A-GPS position method, RNC can get a response within 24 s, and the accuracy is the best among the three methods. The response for this method, however, is slowest among the three methods. And this approach also needs UE support GPS.